1. Field of the Invention
The present invention relates to an antenna apparatus used in Ultra Wide Band (UWB) communication.
2. Description of the Related Art
UWB communication enables an ultra fast communication by using a GHz frequency band. In 2002, the U.S. Federal Communication Commission (FCC) approved usage of the UWB. Since then, an application of the UWB to a portable electronic device and a high precision positioning system has been expected. An ultra wide frequency band antenna apparatus, which includes a teardrop-shaped antenna element and is suitable for a GHz frequency band, has been developed.    Patent Document 1: Japanese Patent Laid-Open Publication No. 2004-129209
A conventional antenna apparatus which includes the teardrop-shaped antenna element provides uniform directivity in 360 degrees, because the antenna element has a uniform shape in planar view.
However, in a case where a communication device with which the antenna apparatus communicates is settled and the direction or the location of the communication device is known, the uniform characteristics in 360 degrees may not be required. In such a case, the conventional antenna apparatus which provides the uniform directivity in 360 degrees may be influenced by noise from a noise source located in a direction which is not necessary for a UWB communication, or may cause noise in an electronic device which does not communicate with the conventional antenna apparatus.
Although it is a technical feature of an antenna apparatus which includes an antenna element having a teardrop shape to provide uniform directivity in 360 degrees, the antenna apparatus can be used more widely if the antenna apparatus selects communication direction.